Process for making load limiting yarn

Abstract

The present invention provides a yarn having a force-displacement profile such that: (a) when the yarn is subjected to an initial stress barrier of from about 0.8 gram/denier to less than or equal to about 1.2 grams/denier, the yarn elongates to less than 5 percent and has an initial modulus in the range from about 30 grams/denier to about 80 grams/denier; (b) upon subjecting the yarn to greater than the initial stress barrier and to less than or equal to about 1.5 grams/denier, the yarn elongates further to at least about 8 percent; and (c) upon subjecting the yarn to greater than 1.5 grams/denier, the modulus increases sharply and the yarn elongates further until the yarn breaks at a tensile strength of at least about 6 grams/denier, wherein the yarn comprises a multiplicity of fibers, all of the fibers have substantially the same force-displacement profile, and are made from polymers having a glass transition temperature in the range from about −40° C. to about +70° C. The present invention also provides a process for making block copolymer and a process for making load limiting yarn from the block copolymer. Webbing from the present yarn is useful for seat belts, parachute harnesses and lines, shoulder harnesses, cargo handling, safety nets, trampolines, safety belts or harnesses for workers at high attitudes, military arrestor tapes for slowing aircraft, ski tow lines, and in cordage applications such as for yacht mooring or oil derrick mooring.

What is claimed is:  
     
       1. Cordage made of copolymer comprising: 
       (a) a first block of polyester wherein said first block is made from an aromatic polyester having: (I) an intrinsic viscosity which is measured in a 60/40 by weight mixture of phenol and tetrachloroethane and is at least about 0.8 deciliter/gram and (ii) a Newtonian melt viscosity which is measured by capillary rheometer and is at least about 7,000 poise at 280° C.; and  
       (b) a second block of polyester wherein said second block is made from lactone monomer and said copolymer has a melting point of at least about 230° C.  
     
     
       2. The cordage of  claim 1  wherein said aromatic polyester is selected from the group consisting of poly(ethylene terephthalate); poly(ethylene naphthalate); poly (alkylene naphthalates); and poly (cycloalkylene naphthalates). 
     
     
       3. The cordage of  claim 1  wherein said aromatic polyester is selected from the group consisting of poly(ethylene terephthalate). 
     
     
       4. The cordage of  claim 1  wherein said aromatic polyester is selected from the group consisting of poly(ethylene naphthalate). 
     
     
       5. The cordage of  claim 3  wherein said first block is made from aromatic polyester having an intrinsic viscosity of at least about 0.9 deciliter/gram. 
     
     
       6. The cordage of  claim 4  wherein said first block is made from aromatic polyester having a Newtonian melt viscosity of at least about 15,000 poises at 280° C. 
     
     
       7. The cordage of  claim 1  wherein said lactone polymer is made from monomer selected from the group consisting of ε-caprolactone, propiolactone, butyrolactone, and valerolactone. 
     
     
       8. The cordage of  claim 1  wherein said cordage is oil derrick mooring.